Implantable components of medical systems, particularly those adapted to provide cardiac pacing and/or defibrillation, often include medical devices coupled to an elongate and flexible electrical lead that carries a plurality of conductors, each of which is typically coupled to a corresponding lead electrode. An implanted cardioverter defibrillator device (ICD) can both detect and classify abnormal heart rhythms, for example, tachycardia and fibrillation, sensed by an implanted multipolar lead, and deliver the appropriate therapy, for example, pacing and/or shock therapy, according to the classification, via the same lead. ICD's may further be programmed to store electrocardiograms (EGM's) of the cardiac signal sensed by the lead over a period of time leading up to and during detection and classification of the signal and following delivery of the therapy. These EGM's can be transferred from the implanted device to an external component (e.g. a programmer/analyzer device or a remote follow-up monitor linked to a network) of the medical system for analysis by an attending physician or clinician.
In some cases the implanted lead can be subject to oversensing, that is, picking up additional signals, either cardiac or non-cardiac, that can cause the device to detect an arrhythmia which is not really present and make an improper classification leading to inappropriate therapy. Commonly assigned and co-pending U.S. patent application publication No. 2003/0204215, entitled “Method and Apparatus for Identifying Cardiac and Non-Cardiac Oversensing Using Intracardiac Electrograms”, describes methods for identifying oversensing, and a series of methods for analyzing EGM's stored by an implantable device following the initial identification of oversensing.
The stored-EGM analysis methods described by U.S. 2003/0204215 serve to categorize the type of oversensing so that appropriate corrective action may be taken; the methods described can determine whether the oversensing is cardiac or non-cardiac in nature, and if non-cardiac in nature, otherwise called ‘noise’, whether the source of the noise is caused by oversensing of myopotentials from muscles adjacent the heart, caused by electromagnetic interference, or caused by some kind of failure that has taken place within the implantable components of the system. However, once the noise is identified as emanating from the system, there may still be questions as to the best course of corrective action. Having the capability to identify particular potential sources of noise in the system can further guide the clinician in a course of action (e.g. adding a new lead to the system to supplement or replace an implanted lead). Thus, there is a need for methods to identify potential sources of noise emanating from within implantable components of a medical system.